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From: Rolf Mantel <news@hartig-mantel.de>
Newsgroups: rec.bicycles.tech
Subject: Re: bike light optics
Date: Wed, 10 Apr 2024 15:32:03 +0200
Organization: A noiseless patient Spider
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Am 10.04.2024 um 14:36 schrieb Roger Merriman:
> Rolf Mantel <news@hartig-mantel.de> wrote:
>> Am 09.04.2024 um 18:59 schrieb Roger Merriman:
>>> Rolf Mantel <news@hartig-mantel.de> wrote:
>>>> Am 09.04.2024 um 07:57 schrieb Jeff Liebermann:
>>>>> On Fri, 5 Apr 2024 09:36:27 -0700, sms <scharf.steven@geemail.com>
>>>>> wrote:
>>>>>
>>>>>> What would be nice is a higher-end battery powered light that could be
>>>>>> charged with a dynamo, and operate at lower power directly from the
>>>>>> dynamo, but there is no such animal. A dynamo to USB-C PD adapter would
>>>>>> be perfect but all the dynamo USB commercial products are to 5VDC only.
>>>>>
>>>>> Good idea, but the dynamo might need to be enlarged to handle the
>>>>> combined load of charging the battery and powering the light.  It is
>>>>> possible to do both with the existing 3 watt dynamos using PWM (pulse
>>>>> width modulation), where the waveforms for powering the light and
>>>>> charging the battery are interlaced so that the dynamo sees only one
>>>>> load at a time.
>>>>
>>>> <https://nabendynamo.de/produkte/ladelux/>
>>>> will go to market this summer.
>>>>
>>> Seems to be claiming 12 watts from the dynamo somehow? Which unless it’s
>>> using the buffer battery that’s going to increase the rolling resistance
>>> significantly ie 4 fold and at that point likely to be quite noticeable.
>>
>> Cheap hub dynamoes have a rolling resistance in the order of 15W to
>> generate 3W.  A good hub dynamo can probably get those 12W out of a
>> mechanical resistance in the order of 20W.
>>
> It’s claiming to draw 12 watts from the dynamo which they generally top out
> at 3 watts, as most of the hubs on the sites claim as an output.

A normal dynamo is rated "3 watts at 6 Volts sinus AC".  If you run the 
dynamo at 12 Volts, you'll be able to pull more energy out of the same 
dynamo at high speed, even with "standard" light bulbs (e.g. a dynamo 
can run two halogen lamps in series, both emitting as much light as a 
normal halogen lamp once your speed exceeds 10 mph).

When using LED instead of light bulbs, the situation becomes a lot more 
complicated.  The exact details of generator electronics are too 
complicated for me to understand.

Rolf